Self-locking fastener and tool for making same

ABSTRACT

A self-locking fastener includes a male member, such as a bolt, having a standard, helical, male thread of constant diameter which is deformed by the special female locking threads of a female member, such as a nut. The female threads are defined by leading and trailing flanks which converge to provide a truncated root that frictionally engages and deforms a portion of the male crest. The trailing flanks of the male and female threads are inclined at the same angle and frictionally engage each other throughout their entire depth. The leading flanks of the male and female threads diverge away from each other to provide a space adjacent the truncated female root for receiving the deformed portion of the male crest therewithin. The deformed portion of the male crest and the full engagement of the trailing flanks produces firm metal-to-metal contact between the members throughout the entire length of the female thread, thereby procluding lateral movement of one member relative to the other. A tapping tool having a male thread which is the mirror image of the female thread to be formed is employed to produce the thread form in the female member.

TECHNICAL FIELD

The present invention generally relates to locking fasteners of the threaded type, and deals more particularly with a male and female thread construction in which the male thread is deformed during mating of the members to produce locking of the fastener.

BACKGROUND ART

Standard manufacturing tolerances inherent in the threaded portions of conventionally threaded fasteners result in small air spaces between the mated male and female threads which allow the tener combination to shift laterally or "rock" when subjected to vibration or shock. This lateral movement of the threads is sufficient to overcome starting friction between those portions of the threads which are in frictional contact with each other. When the fastener is tightened, a substantial amount of potential energy is stored in the threads (due to stresses), which is transformed in kinetic energy as the threads laterally shift with respect to each other, thereby unlocking the threads and loosening the fastener. This undesirable situation is particularly acute in assemblies which are subjected to constant vibration, such as steering assemblies, drivetrains, engines, etc.

Numerous locking thread constructions have been devised in the past in an effort to overcome the problems mentioned above. Some of these past attempts have involved the forming of the threads during the assembly process in order to increase friction between the male and female threads. For example, one typical locking thread construction is shown in my prior U.S. Pat. No. 4,150,702 which discloses a fastener combination in which conventional male threads are deformed when mated with a special female thread. Although this previous fastener combination is suitable for many applications, it is less than completely desirable in some cases since not all of the male threads mating with the female threads are deformed. Additionally, the amount of surface contact between the male and female threads is limited to that portion of the male threads which is in fact deformed, i.e., substantial flank-to-flank contact is not achieved.

Accordingly, it is a primary object of the present invention to provide a selflocking fastener which eliminates lateral or radial type movement of the threads relative to each other, in which tight frictional engagement is achieved between the male and female threads throughout the entire length of the female thread.

Another object of the invention is to provide a fastener of the type described above in which a portion of the male thread is deformed when the fastener members are assembled, but yet which also provides firm frictional engagement between one pair of opposing flanks of the male and female thread.

Another object of the invention is to provide a fastener of the type described above which eliminates the need for close manufacturing tolerances for the threads and which employs a standard male thread of constant diameter.

These, and further objects of the invention, will be made clear or will become apparent during the course of the detailed description thereof set out below.

DISCLOSURE OF THE INVENTION

In accordance with the present invention a self-locking fastener assembly comprises a male member, such as a bolt, having a standard helical male thread of constant diameter and a female member provided with a special, locking, female thread threadably mateable with the male thread to produce an interference fit in which a portion of the male thread is deformed to assure firm metal-to-metal contact between the mating threads. The female thread is defined by leading and trailing flanks which converge to provide a truncated root which frictionally engages, and deforms a portion of a male crest defined by leading and trailing flanks of the male thread. The trailing flanks of the male and female threads are inclined at the same angle in order to produce firm frictional engagement with each other essentially throughout their depth. The leading flanks of the male and female threads diverge away from each other to define a space adjacent the truncated female root for receiving the deformed portion of the male crest therewithin. In the preferred form of the invention, the angle of divergence between the leading flanks of the male and female threads is between about 5 and 20 degrees. The female thread is produced by a tapping tool having a male thread thereon which is a complement of the female thread to be formed.

BRIEF DESCRIPTION OF THE DRAWINGS

In the drawings, which form an integral part of the specification and are to be read in conjunction therewith, and in which like components are designated by identical reference numerals in the various views:

FIG. 1 is a fragmentary longitudinal view of a fastener assembly which forms the preferred embodiment of the present invention, parts of the male and female members being broken away in section to reveal the mating thread forms;

FIG. 2 is an enlarged view of the mating thread forms shown in FIG. 1;

FIG. 3 is a longitudinal view of a tool for producing the female thread in the female member, and shown in operative relationship to a female member being tapped;

FIG. 4 is a view of one end of the tool shown in FIG. 3; and

FIG. 5 is an enlarged view of the thread on the tool shown in FIGS. 3 and 4, in operative relationship to the female member being tapped.

BEST MODE FOR CARRYING OUT THE INVENTION

Referring first to FIGS. 1 and 2, the present invention is generally concerned with a fastener assembly, generally indicated by the numeral 10, which includes a threaded male member, such as a bolt 12 threadably coupled with a threaded female member, such as nut 14. Although the bolt 12 and nut 14 are shown in the drawings for purposes of simplicity, it may be appreciated that the male member may comprise a threaded stud formed integral with a larger part, while the female member may comprise a tapped hole in a part.

The bolt 12 is provided with a head 18 adapted to receive a wrench or the like, and an elongated shank 16 extending outwardly from the head 18. Shank 16 is provided with a helical, male thread 20 formed thereon. Male thread 20 is defined by trailing and leading flanks 24 and 28 respectively which converge to define a male thread crest 34 and male thread root 38. The trailing and leading flanks 24 and 28 are inclined relative to the longitudinal axis 44 of the shank 16 at substantially the same angle, throughout the entire length of the male thread 20. Thus, male thread 20 is of a standard type which is symmetric in cross-section, i.e. the thread is symmetric about a reference line extending normal to axis 44 and passing through the intersection of the trailing and leading flanks 24 and 28 respectively.

The nut 14 comprises a cylindrically shaped body having a hole therethrough and within which a special female thread 22 is defined. The female thread 22 is defined by trailing and leading flanks 26 and 30 respectively which converge to form a female root 39 at the outer diameter of the thread 22, and a female crest 36 near the inner diameter of thread 22. The female root 39 receives the male crest 34 therein, while the female crest 36 is received within male root 38.

The female thread 22 is of an asymmetric type in which the trailing and leading flanks 26 and 30 are inclined at differing angles relative to the longitudinal axis 44 and are asymmetrically disposed about an axis 46 which extends normal to axis 44 and passes through the point of intersection of flanks 26 and 30 defined by extension lines 26a and 30a. The leading flank 26 is inclined with respect to axis 46 an angle φ, while the leading flank 30 is inclined with respect to axis 46 at an angle ψ. It may be readily appreciated that angles φ and ψ are directly proportional to the inclination of flanks 26 and 30 relative to the longitudinal axis 44. Angle ψ is within the range of 10 to 20 degrees, and preferably approximately 15 degrees. Also, in the preferred form of the invention, the angle φ exceeds angle ψ by an amount which is the range of 5 to 20 degrees; the maximum, however, is approximately 25 degrees. In any event, the trailing flanks 24 and 26 of the respective threads 20 and 22 are inclined at the same angle relative to each other, while the leading flanks 28 and 30 diverge radially outward, away from each other. Since the male thread 20 is symmetric, it may be appreciated that the angle between the leading flanks 28 and 30 is equal to the difference between the angles φ and ψ, i.e. 5 to 20 or 25 degrees in the preferred form. The female root 39 is truncated by an essentially flat root surface 40 which extends transversely between the trailing and leading flanks 26 and 30. The outside diameter of the male thread 20 exceeds that of the female thread 22. In other words, the distance between the longitudinal axis 44 and the male crest 34 is greater than that between axis 44 and root surface 40. The divergence of leading flanks 28 and 30 produces a space 32 adjacent the female root 39 for purposes which will become later apparent.

In use, the nut 14 is threaded onto the outer end of shank 16 with the necessary amount of prevailing torque; as the male crest 34 engages the root surface 40 a portion of the crest 34 is deformed laterally at 42 into the space 32 and firmly engages both the root surface 40 and a portion of the leading flank 30. The trailing flanks 24 and 26 are in substantially tight, frictional engagement with each other, substantially throughout their entire depth as a result of axial tension imposed on the threads 20,22 during the threading process. The threading process is continued until the nut 14 reaches the desired location along the length of shank 16. From the above, it may be appreciated that the total surface area of frictional contact between the male and female threads 20 and 22 consists of the area of face-to-face engagement between the leading flanks 24 and 26 in addition to that part of the male crest engaging root surface 40 and outer portions of the leading flank 30. By virtue of the fact that the major diameter of the male thread 20 exceeds that of the female thread 22, lateral stability between bolt 12 and nut 14 is assured since the female root 39 is completely filled by the male crest 34. Longitudinal stability is also assured since the trailing flanks 24 and 26 tightly engage each other on one side of the female thread 22 while the deformed portion 42 firmly engages the leading flank 30.

Referring now also to FIGS. 3-5, the female thread 22 may be formed in the nut 14, or other part, by a tapping tool generally indicated at 48. Tapping tool 48 includes an elongate, generally cylindrical body 50 having a male thread 52 formed on one extremity thereof. Male thread 52 is essentially a mirror image of female thread 22 and is defined by trailing and leading flanks 58 and 60 which converge to form a crest 62 and root 64. The crest 62 is truncated by flat 56 which extends transversely between the trailing and leading flanks 58 and 60. Flanks 58 and 60 are inclined at different angles relative to the longitudinal axis 66 of body 50, consequently the male thread 52 is asymmetric in cross-section. As shown in FIG. 5, trailing flank 58 is inclined relative to a line 68 which is normal to axis 66 at an angle φ which is greater in magnitude than the angle ψ between lines 68 and flank 60. As in the case of the female thread 22, the difference between angles φ and ψ may range from about 5 to about 25 degrees. Body 50 may include a plurality of circumferentially spaced, longitudinally extending slots 54 in the surface thereof which interrupt the male thread 52 in order to accommodate metal cuttings generated during the tapping process.

As indicated in FIGS. 1 and 3, it is advantageous to include one or two full depth threads in the nut to start the engagement of the nut and bolt. This is accomplished by including a full height portion on the tap 48 and running the tap into the nut a controlled distance.

As will be apparent to those skilled in the art, the thread forms are shown in somewhat idealized form, i.e., the sharp peaks and valleys are not as distinct in actual practice nor are the fits as perfect as shown due to tolerances and limitations of actual mechanical components.

Finally, the terms "leading" and "trailing" are arbitrary, but "trailing" is selected to designate the flanks which converge under axial load.

From the foregoing, it may be appreciated that the self-locking fastener and tool for making same described above not only provide for the reliable accomplishment of the objects of the invention but do so in a particularly effective and economical manner. It is recognized, of course, that those skilled in the art may make various modifications or additions to the preferred embodiment chosen to illustrate the invention without departing from the spirit and scope of the present contribution to the art. Accordingly, it is to be understood that the protection sought and to be afforded hereby should be deemed to extend to the subject matter claimed and all equivalents thereof fairly within the scope of the invention. 

What is claimed is:
 1. For use with a male threaded fastener member having leading and trailing flanks converging to define a male thread which is symmetric in cross-section and constant in diameter, a female threaded member matingly threadable with said male member comprising:a body having a female thread formed therein, said female thread being asymmetric in cross-section and defined by leading and trailing flanks converging toward each other at differing angles relative to the longitudinal axis of said female thread to provide a female threat root, said thread root including means for deforming a portion of said male thread upon threaded mating of said male and female members, said leading flanks of said male and female threads including a space therebetween for receiving said portion of said male thread therewithin, said trailing flanks of said male and female thread being in face-to-face frictional engagement along essentially the entire depths thereof, said female thread root being of constant diameter throughout at least a portion of the length of said female thread and said deforming means includes an essentially flat root surface extending transversely between said leading and trailing flanks of said female thread, said leading flank of said female thread being inclined from a reference line extending normal to said longitudinal axis at an angle of approximately 15 degrees.
 2. The female threaded fastener member of claim 1, wherein said leading and trailing flanks of said male thread and said trailing flank of said female thread are each inclined with respect to said longitudinal axis at first angle and said leading flank of said female thread is inclined with respect to said longitudinal axis at a second angle, said first angle differing in magnitude from said second angle by an amount in the range between approximately 5 to 25 degrees.
 3. The female threaded member of claim 1, wherein said leading flanks of said male and female threads respectively diverge away from each other at an angle within the range of 5 to 25 degrees.
 4. The female threaded member of claim 3, wherein the major diameter of said male thread is greater in magnitude than the major diameter of said female thread, and the leading flank of said female thread is inclined away from a line extending normal to said longitudinal axis at an angle in the range of 10 to 20 degrees.
 5. The female threaded member of claim 1, wherein said body includes a nut having surface areas adapted to be lockingly engaged by a wrench.
 6. For use in a self-locking fastener combination of the type including a male fastener member having a standard helical thread formed thereon defined by leading and trailing flanks converging toward each other to provide a male thread crest, a female fastener member matingly threadable with said male member, comprising:a body having a thread formed therein including leading and trailing flanks respectively opposing the leading and trailing flanks of said male member and converging toward each other to provide a female root for receiving said male crest therein, said female root being truncated to define a root surface extending transverse between the leading and trailing flanks of said female member, the distance between the longitudinal axis of said fastener combination and said male crest being less in magnitude than the distance between said axis and said root surface whereby to produce firm frictional engagement between said male crest and said root surface and deformation of a portion of said male crest when said male and female members are threaded together, at least a part of the leading flank of said female thread being spaced from the opposing leading flank of said male thread at a location adjacent said root surface to provide an open area adjacent said male crest for receiving the deformed portion of said male crest therewithin, the trailing flanks of said male and female threads extending essentially parallel to each other and being in substantially face-to-face frictional engagement with each other, said root surface being essentially flat and extending substantially parallel to said longitudinal axis.
 7. The female fastener member of claim 6, wherein said leading flanks of said male and female threads diverge away from each other at an angle between 5 and 25 degrees.
 8. The female fastener member of claim 6, wherein said body includes a nut and said root surface extends the entire length of said female thread.
 9. A female fastening component for threadably mating with a male fastening component having a standard threadform thereon defined by leading and trailing flanks coverging to define a male thread crest, said leading and trailing flanks being oppositely inclined at essentially equal angles relative to the longitudinal axis of said male component, comprising:a body having a female thread formed therein, said female thread having leading and trailing flanks converging to define a female thread root for receiving said male crest therewithin, said leading and trailing flanks of said female thread being oppositely inclined with respect to said longitudinal axis at respectively differing angles whereby said female thread is asymmetric in cross-section to define an open space between opposing leading flanks of said male and female thread respectively, said female root being truncated and including an essentially flat root surface extending transversely between opposing leading and trailing flanks of said female thread, the radius of said root surface relative to said longitudinal axis being less in magnitude than the radius of said male thread crest, whereby said male thread firmly engages and has a portion thereof deformed by said root surface upon threading male and female components with each other, said deformed portion of said male thread crest being received within said open space.
 10. The female fastening component of claim 9, wherein the difference between the leading and trailing flank angles of said female thread is between approximately 5 and 25 degrees.
 11. The female fastening component of claim 10, wherein the trailing flanks of said male and female threads are inclined at substantially the same angle relative to said longitudinal axis and frictionally engage each other essentially along the entire respective depths thereof, the leading flank of said female thread being inclined relative to said longitudinal axis at an angle of approximately 75 degrees.
 12. The female fastening thread of claim 9, wherein said female thread root is of substantially constant radius relative to said longitudinal axis through out at least a portion of the length of said female thread.
 13. A prevailing-torque fastener assembly, comprising:a male fastener member having a helical male thread formed thereon, said male thread being defined by leading and trailing flanks converging to define a male thread crest of substantially constant diameter over the entire length of said male thread, a female fastener member having a female thread formed therein for threadably receiving said male fastener member, said female thread being defined by leading and trailing flanks converging to provide a female thread root within which said male thread crest may be received, said female thread crest when said male and female fastener members are threaded together, the trailing flanks of said male and female threads being inclined at a first angle relative to the longitudinal axis of said fastener combination and frictionally engaging each other, the leading flanks of said male and female threads diverging away from each other at respective second and third angles to define an open space adjacent said female root within which said portion of said male thread crest may be received, said second angle being substantially equal in magnitude to said first angle, said third angle being less in magnitute than said second angle, said deforming means including a substantially flat root surface extending between the leading and trailing flanks of said female thread, the major diameter of said female thread being less in magnitude than that of the major diameter of said male thread whereby said male thread crest firmly engages said root surface.
 14. The fastener assembly of claim 13, wherein the difference in the magnitude of said second and third angles in the range of 5 to 25 degrees.
 15. The fastener assembly of claim 13, wherein said male fastener member includes a bolt and said female fastener member includes a nut.
 16. For use with a male threaded fastener member having helical thread having leading and trailing flanks converging to define a male thread which is symmetric in cross-section and having a crest which is constant in diameter, a female threaded member matingly threadable with said male member comprising:a body having a female thread formed therein, said female thread being asymmetric in cross-section and defined by leading and trailing flanks converging toward each other at differing angles relative to the longitudinal axis of said female thread to provide a thread space having a bottom root surface disposed at a constant diameter less than the diameter of the crest of the thread of the male member and radially engageable therewith when the members are threaded together, the different angles between opposite sides of the female thread providing a space between the leading flanks of both threads adjacent the crests of the male thread, the trailing flanks of the threads extending at the same angle to provide essentially full contact throughout their overlapped radial extent under load. 